Induction of Ocular Surface Regeneration

Abstract

junctiva, and the intervening transition area (the limbus) (Figure 20.1). The avascular cornea is continuous with the sclera, forming together the outer envelop of the eyeball [Figure 20.1 and 20.2 (see color section)]. The transparent cornea is the gateway for the entrance of images into the eye, and accounts for more than two thirds of the total refractive power of the eye. The cornea consists of five layers: The epithelium, Bowman’s layer, the stroma, Descemet’s membrane, and the endothelium. The corneal transparency is essentially maintained by its avascularity, an intact epithelium, and a normal morphology and function of its other layers. These components of the ocular surface are essential for vision, the integrity of the eye, and for preventing ocular infections. Injury to the ocular surface may be caused by physical or chemical agents, infectious, oculocutaneous disorders, drugs, or systemic disorders. A variety of physical agents may induce tissue damage: Thermal burns, microwaves, lasers, ionizing radiation. Chemical agents are a common cause for severe ocular surface injury: Acids tend to precipitate tissue proteins and cause coagulation and necrosis, thus creating a barrier against deeper penetration, and damaging mainly the external eye; in alkali burns, the hydroxyl ions saponify lipids in the corneal epithelium, denature proteins, and cause tissue melting and may penetrate into the deeper layers. Various microorganisms may be associated with damage to the ocular surface, such as herpes zoster virus that may cause a chronic conjunctivitis with submucosal scarring, hypoesthesia, and lid impairment caused by cicatrization. Chlamydia trachomatis (serotypes A, B, Ba, and C) is a major cause for blindness in developing countries because of the infection of conjunctival cells that initiates an inflammatory response with fibrosis of the subconjunctival tissue, and cicatrizing process of the external eye. A wide range of dermatologic conditions are associated with ocular surface injury. They include mainly ocular cicatricial pemphigoid and Stevens-Johnson syndrome. In ocular cicatricial pemphigoid, a condition with an autoimmune origin, chronic conjunctival inflammation is progressive with exacerbations; the disease is usually bilateral and can lead to severe scarring of the conjunctiva and adherence between bulbar and palpebral conjunctiva (symblepharon) with limitation of ocular motility and to vascularization of the cornea, which may progress to blindness. The ocular manifestations of StevensJohnson syndrome are a pseudomembranous conjunctivitis in the acute stage, and in the later phase, conjunctival cicatrization with involvement of the limbus and the cornea are predominant. Moreover, genetic diseases such as aniridia also result in disruption of the normal ocular surface. Ocular surface reconstruction (OSR) has recently become a common methodology in the regenerative treatment of severe ocular surface disease. The challenge in this field was motivated by the necessity to find a cure for patients as mentioned above, affected by severe and difficult 20